Abstract
This study aimed to examine the effects of exercise-induced increases in skeletal muscle contractile performance on isolated skeletal muscle caffeine sensitivity in mice. CD1 mice (n=28; 30 weeks old) either served as controls or underwent 8 weeks of voluntary wheel running. Following the treatment intervention, whole soleus (SOL) or a section of the costal diaphragm (DIA) was isolated from each mouse and tested to determine the effect of 70 µmol l-1 caffeine on work loop power output. Although caffeine elicited a significant increase in power of both the SOL and the DIA relative to levels in a non-caffeine-treated control, the effect was not different between the experimental groups, despite the muscles of the trained group producing significantly greater muscle power. There was no significant relationship between training volume or baseline work loop power and the caffeine response. These results indicate that an exercise-induced increase in muscle performance did not influence the performance-enhancing effects of caffeine.
Highlights
Despite a wealth of research documenting the performanceenhancing effects of caffeine on exercise performance in humans, evidence is still contentious
Despite a substantial training-induced increase in muscle power output of >25% for both SOL and DIA muscles, 8 weeks of voluntary wheel running failed to elicit a change in the caffeine-induced increase in muscle power when compared with untrained controls
These data demonstrate for the first time that, at the muscle level, the ergogenic effect of caffeine cannot be improved by exercise training
Summary
Despite a wealth of research documenting the performanceenhancing effects of caffeine on exercise performance in humans (for reviews, see Graham, 2001; Astorino and Roberson, 2010), evidence is still contentious. One such area of uncertainty is whether caffeine elicits a greater performance-enhancing benefit in trained compared with untrained individuals. There is evidence to suggest that caffeine can act directly on skeletal muscle, at least in rodents and amphibians, to promote elevated power output (Tallis et al, 2015). What is not clear is to what extent the potential for increased caffeine sensitivity in trained individuals is related to a greater
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